Dearly beloved, we are gathered here today to remember that “Purple Rain” is the greatest music movie of them all. Thirty years ago Sunday, Prince’s big-screen debut was released into theaters, telling the semi-autobiographical story of “the Kid” — a talented Minneapolis musician trying to make it to the big time while dealing with family troubles and his own insecurities.

In fairness, Prince was never a threat to De Niro in terms of acting ability. But the music sequences were, and still are, mind-blowing — and led the film to earn nearly $70 million at the box office (almost 10 times what it cost). The soundtrack album was No. 1 on the Billboard album chart for a remarkable 24 consecutive weeks, from the summer of 1984 into early 1985. Additionally, it spawned two No. 1 hit singles with “When Doves Cry” and “Let’s Go Crazy.” At one point, Prince had the No. 1 single, No. 1 album and No. 1 movie in the country. To mark the anniversary of “Purple Rain,” here are 10 things you probably didn’t know about Prince’s crowning achievement.

1. The part of Prince’s love interest in the film was initially given to Denise Matthews, a k a Vanity. She was a member of Vanity 6 — a girl-band put together and controlled by Prince — but pulled out of the film at the last minute. Many speculate that she and Prince were dating and had a blowout, but director Albert Magnoli claims it was because she was offered a role in Martin Scorsese’s “The Last Temptation of Christ” (her role in that film ended up on the cutting room floor).

Vanity 6, with Denise Matthews center.Photo: WireImage

2. After Vanity left the project, her role was offered to Jennifer Beals of “Flashdance” fame — but she turned it down because she wanted to go to college. (Beals went on to earn a degree in American literature from Yale in 1987.)

Jennifer BealsPhoto: Getty Images

3. The role finally went to Apollonia Kotero, who was dating Van Halen’s David Lee Roth at the time. Prince demanded the couple break up so fans would speculate on whether Apollonia and Prince’s on-screen relationship was real. (She complied.) He also demanded that she didn’t publicly date anyone during the film’s promotion.

4. Revolution guitarist Wendy Melvoin and keyboardist Lisa Coleman were a couple during the filming of “Purple Rain,” but it was never publicly confirmed or denied at the time. Rumors have it that a scene in which they kiss was cut from the final edit. What is true is the fact that they stayed together for 20 years in total.

Lisa Coleman and Wendy Melvoin at the premiere of Prince’s “Cherry Moon” in 1986.Photo: Redferns/Getty Images

5. The famous scene in which Apollonia gives in to the Kid’s cruel request and purifies herself in the waters of Lake Minnetonka almost caused her to contract hypothermia. The scene was shot on a freezing November day, and after the fourth take, Kotero started to black out from the cold. She came around after warming up with blankets and a few hugs from Prince himself.

Kotero and PrincePhoto: Everett Collection

6. Although he almost stole the film with his own charismatic performance as Prince’s nemesis, Morris Day of the Time was lucky to be in it at all. Friends since high school, Prince and Day’s relationship had been souring: The Time were controlled by and had their songs written by Prince, and the arrangement came to frustrate Day. That tension resulted in an on-set fight that was broken up by the Time’s drummer Jellybean Johnson.

Morris DayPhoto: Everett Collection

7. The film’s producers had four weeks scheduled to shoot the music performances of “Purple Rain” at the First Avenue club in Minneapolis. However, because Prince and the Revolution were such a tight band, they only needed a week to get everything in the can.

8. Several songs from the “Purple Rain” soundtrack were recorded live during a benefit performance at First Avenue in August 1983. If you listen closely — especially to the title track — you can actually hear the crowd on the recording. Prince rerecorded the vocals and edited out an extra verse to make the version that appears on the album and in the film.

KoteroPhoto: Everett Collection

9. The eight-minute title track of the film and album was originally even longer — and Prince initially requested that his friend Stevie Nicks write the lyrics for it. The Fleetwood Mac singer declined his offer, saying that she found the track too “overwhelming” and let him finish it. Great decision, Stevie!

Stevie Nicks in 1983.Photo: WireImage

10. Remember those “Parental Advisory” stickers that used to come on CDs, warning of adult content? That was something that began partly because of the “Purple Rain” soundtrack. Tipper Gore (then-wife of Al) founded the Parents Music Resource Center in 1985 after hearing “Darling Nikki” — with its references to masturbation — playing on her 11-year-old daughter’s stereo. The song became one of the “Filthy Fifteen” the PMRC committee objected to, along with Cyndi Lauper’s “She Bop” and Madonna’s “Dress You Up.” After a Senate hearing, the Record Industry Association of America agreed to use their own discretion to label potentially offensive music. Just another of the countless ways Prince changed music.